This invention relates to proteins having fibrinolytic and coagulation-inhibiting properties, which are linked at the N- and/or C-terminal end of the plasminogen-activating amino acid sequence to a thrombin- or factor Xa-inhibiting amino acid sequence, to plasmids for producing these polypeptides, and to thrombolytic agents which contain a polypeptide of this type as their active ingredient.
There are several serious diseases which are caused by the occlusion of arterial or veinous blood vessels. These thrombotic diseases include coronary thrombosis, cerebral thrombosis, pulmonary embolism, deep veinous thrombosis and peripheral arterial occlusion diseases Due to the occlusion of the blood vessels the supply of oxygen to the corresponding tissue and the exchange of nutrients and metabolites are interrupted, so that irreversible damage to the organ or tissue concerned may result.
The occlusion of a blood vessel caused by a thrombus mainly occurs at an arteriosclerotic lesion comprising fibrin, thrombocytes and erythrocytes under the action of various enzymes of the blood coagulation system. Within the enzyme cascade of the coagulation system, factor Xa and thrombin play a prominent role. Factor Xa, as a constituent of the prothrombinase complex, converts prothrombin to thrombin. Thrombin can activate all the important enzymes of the coagulation system, can induce the aggregation of thrombocytes and can lead to the formation of a fibrin network by the conversion of fibrinogen to fibrin (Furie and Furie in New Engl. J. Med. 326, 800 (1992)).
The formation of thrombuses is restricted by physiological anticoagulants, for example antithrombin III, activated protein C and tissue factor pathway inhibitor. Once formed, thrombuses can be re-dissolved by the action of plasmin occurring naturally in the body. Plasmin is formed from an inactive proenzyme, plasminogen, which is proteolytically activated by plasminogen activators. The thrombolysis due to plasmin is utilised therapeutically, by treating patients with thrombotic diseases, particularly patients with acute coronary thrombosis, with plasminogen activators. Streptokinase, APSAC (an isolated plasminogen streptokinase activator complex), double-chain urokinase (UK), recombinant single-chain urokinase (recombinant prourokinase) and tissue plasminogen activator (t-PA) are currently available for this therapy (Collen and Lijnen in Blood 78, 3114, (1991)). The following are under development: bat plasminogen activators (Gardell et al. in J. Biol. Chem. 264, 17947 (1989); EP 383 417), staphylokinase (Schlott et al. in Bio/Technology 12, 185 (1994) ; Collen and Van De Werf in Circulation 87 1850 (1993)), the recombinant tissue plasminogen activator BM 06.022 (Martin et al. in J. Cardiovasc. Pharm. 18, 111 (1991)) and the t-PA variant TNK-t-PA (Keyt et al. in Proc. Natl. Acad. Sci. 91, 3670 (1994)).
Streptokinase, a protein of haemolytic streptococci, activates human plasminogen, in that it forms a complex with plasminogen and thereby converts the plasminogen into an active conformation. This complex itself converts free plasminogen to plasmin, which then in turn cleaves the plasminogen bound to streptokinase. Staphylokinase, a protein obtained from Staphylococcus aureus, also acts similarly, but possesses a higher fibrin specificity compared with streptokinase. APSAC, a compound of streptokinase and human plasminogen which is produced in vitro, is a further development of streptokinase. Due to a chemical modification of the active center of the plasminogen, APSAC has a biological half-life which is longer than that of streptokinase.
Urokinase is a human protein which can be obtained in two forms as a proteolytically active protein from urine; high molecular weight urokinase (HUK) and low molecular weight urokinase (LUK) (Stump et al. in J. Biol. Chem. 261, 1267 (1986)). HUK and LUK are active forms of urokinase, i.e. double-chain molecules. Urokinase is formed as single-chain urokinase (prourokinase) in various tissues and can be detected in small amounts as a proenzyme in human blood (Wun et al. in J. Biol. Chem. 257, 3276 (1982)). As HUK, the activated form of prourokinase has a molecular weight of 54 kilodaltons and consists of 3 domains: the amino-terminal growth factor domain, the kringle domain and the serine protease domain (Guenzler et al. in Hoppe-Seyler's Z. Physiol. Chem. 363, 1155 (1982); Steffens et al. in Hoppe-Seyler's Z. Physiol. Chem. 363, 1043 (1982)). Although prourokinase and plasminogen are present as proenzymes, prourokinase is capable, due to its intrinsic activity, of transforming plasminogen into active plasmin. However, this plasminogen activator does not attain its full activity until the plasmin formed has itself cleaved the prourokinase between .sup.158 lysine and .sup.159 isoleucine (Lijnen et al. in J. Biol. Chem. 261, 1253 (1986)). The production of urokinase in Escherichia coli by genetic engineering was first described by Heyneker et al. (Proceedings of the IVth International Symposium on Genetics of Industrial Microorganisms 1982). Unglycosylated prourokinase (saruplase) is produced using a synthetic gene (Brigelius-Flohe' et al. in Appl. Microbiol. Biotech. 36, 640 (1992)).
t-PA is a protein with a molecular weight of 72 kilodaltons which is present in blood and in tissue. This plasminogen activator consists of 5 domains: the amino-terminal finger domain, the growth factor domain, kringle domain 1, kringle domain 2 and the serine protease domain. Like prourokinase, t-PA is converted into the active, double-chain form by a plasmin-catalysed cleavage between kringle domain 2 and the serine protease domain, i.e. between .sup.275 Arg and .sup.276 Ile. In vitro studies and the results of experiments on animals indicate that t-PA binds to fibrin and its enzymatic activity is stimulated by fibrin (Collen and Lijnen in Blood 78, 3114 (1991)). The fibrin specificity of t-PA should prevent the formation of plasmin in the entire blood system, resulting not only in the decomposition of fibrin decomposed but also in the decomposition of fibrinogen. A systemic plasminogen activation such as this as well as the extensive decomposition of fibrinogen are undesirable, since this increases the risk of haemorrhage. It has been shown in therapeutic practice, however, that the expectations derived from pre-clinical studies as regards the fibrin specificity of t-PA are not fulfilled. High doses, which result in systemic plasminogen activation despite this fibrin specificity, have to be infused due to the short biological half-life of t-PA (Keyt et al. in Proc. Natl. Acad. Sci. 91, 3670 (1994)).
r-PA and TNK-t-PA are variants of t-PA which possess improved properties. In r-PA (BM 06.022) the first three t-PA domains, i.e. the finger domain, the growth factor domain and the first kringle domain, have been deleted, so that the shortened molecule only contains the second kringle domain and the protease domain. r-PA is produced in Escherichia coli by genetic engineering and is not glycosylated. Compared with t-PA, r-PA has a longer biological half-life and more rapidly leads to reperfusion. It has been shown in experiments on animals that r-PA applied as a bolus is just as effective as a t-PA infusion (Martin et al. in J. Cardiovasc. Pharmacol. 18, 111 (1991)).
The t-PA variant TNK-t-PA differs from natural t-PA on three counts: the replacement of .sup.103 threonine by asparagine, due to which a new glycosylation site is formed; the replacement of .sup.117 asparagine by glutamine, due to which a glycosylation site is removed, and the replacement of the sequence between .sup.296 lysine and .sup.299 arginine by four successive alanine units. The combination of these three mutations results in a polypeptide with a higher fibrin specificity and a longer biological half-life compared with natural t-PA. Moreover, TNK-t-PA is considerably less inhibited by PAI-1 than is natural t-PA (Keyt et al. in Proc. Natl. Acad. Sci. 91, 3670 (1994)). Results obtained from experiments on animals in which a precursor of TNK-t-PA was used indicate that TNK-t-PA is suitable for bolus application (Refino et al. in Thromb. Haemost. 70, 313 (1993)).
Bat plasminogen activator (bat-PA) occurs in the saliva of the Desmodus rotundus bat. This plasminogen activator, which has meanwhile also been synthesized by genetic engineering, has an even more pronounced fibrin specificity than t-PA and in tests on animals has exhibited improved thrombolysis with an increased biological half-life and reduced systemic plasminogen activation (Gardell et al. in Circulation 84, 244 (1991)).
In the treatment of thrombotic diseases, plasminogen activators are generally administered together with an anticoagulant substance, for example heparin. This results in improved thrombolysis compared with treatment with a plasminogen activator only (Tebbe et al. in Z. Kardiol. 80, Suppl. 3, 32 (1991)). Various clinical results indicate that, in parallel with the dissolution of thrombuses, an increased tendency towards coagulation occurs (Szczeklik et al. in Arterioscl. Thromb. 12, 548 (1992) Goto et al. in Angiology 45, 273 (1994)). It is assumed that thrombin molecules which are enclosed in the thrombus and which are released again when the clot dissolves are responsible for this. Moreover, there are indications that plasminogen activators themselves also accelerate the activation of prothrombin and thus act in opposition to thrombolysis (Brommer and Meijer in Thromb. Haemostas. 70, 995 (1993)). Anticoagulant substances such as heparin, hirugen, hirudin, argatroban, protein C and recombinant tick anticoagulant peptide (TAP) can suppress this increased tendency towards re-occlusion during thrombolysis and can thus enhance the success of lysis therapy (Yao et al. in Am. J. Physiol. 262 (Heart Circ. Physiol. 31) H 347-H 379 (1992); Schneider in Thromb. Res. 64, 667 (1991); Gruber et al. in Circulation 84, 2454 (1991); Martin et al. in J. Am. Coll. Cardiol. 22, 914 (1993); Vlasuk et al. in Circulation 84, Suppl. II-467 (1991).
One of the strongest thrombin inhibitors is hirudin from the Hirudo medicinales leech, which consists of 65 amino acids. There are various iso-forms of hirudin, which differ as regards some of their amino acids. All iso-forms of hirudin block the binding of thrombin to a substrate, for example fibrinogen, and also block the active center of thrombin (Rydel et al. in Science 249, 277 (1990); Bode and Huber in Molecular Aspects of Inflammation, Springer, Berlin, Heidelberg, 103-115 (1991); Stone and Hofsteenge in Prot. Engineering 2, 295 (1991); Dodt et al. in Biol. Chem. Hoppe-Seyler 366, 379 (1985). In addition, smaller molecules derived from hirudin are known, which also act as thrombin inhibitors (Maraganore et al. in Biochemistry 29, 7095 (1990); Krstenansky et al. in J. Med. Chem. 30, 1688 (1987); Yue et al. in Prot. Engineering 5, 77 (1992)).
The use of hirudin in combination with a plasminogen activator for the treatment of thrombotic diseases is described in U.S. Patent No. 4,944,943 (=EP 328,957) and U.S. Pat. No. 5,126,134 (=EP 365,468). The use of hirudin derivatives in combination with a thrombolytic agent is known from International Patent Application WO 91/01142.
Hirullin is a protein containing 61 amino acids which is isolated from the Hirudo manillensis leech. Hirullin is identical to hirudin as regards its action and inhibitor strength, but differs very considerably from hirudin as regards its amino acid sequence. It has also proved possible to derive smaller molecules from hirullin, which are very good thrombin inhibitors (Krstenansky et al. in Febs Lett. 269, 465 (1990)).
In addition, thrombin can also be inhibited by a peptide which is derived from the amino-terminal sequence of the human thrombin receptor (Vu et al. in Nature 253, 674 (1991)). The thrombin receptor contains a thrombin-binding sequence, with an adjacent cleavage site for thrombin, in the extracellular, amino-terminal region. This sequence can inhibit thrombin provided that the cleavage site is masked by the replacement of .sup.42 serine by .sup.42 phenylalanine.
Antistasin and TAP are inhibitors of factor Xa. Antistasin is a protein from the Haementeria ghiliani leech, which contains 119 amino acids but has no homology of sequence with hirudin (Tuszynski et al. in J. Biol. Chem. 262, 9718 (1987); Nutt et al. in J. Biol. Chem. 263, 10162 (1988) ; Condra et al. in Thromb. Haemostas. 61, 437 (1989)). The recombinant production of antistasin has been described by Han et al. in Gene 75, 47 (1989).
TAP is a protein containing 60 amino acids from the Onithodoros moubata tick, which can also be produced by genetic engineering. TAP binds reversibly to factor Xa and thus acts in opposition to the formation of thrombin. The efficacy of TAP has been proved to be similar to that of hirudin or heparin in various thrombosis models (Vlasuk in Thromb. Haemost. 70, 212 (1993); Schaffer et al. in Circulation 84, 1741 (1991)).
Phaneuf et al., in Thromb. Haemost. 71, 481 (1994), describe a complex which results from a fortuitous chemical linking of streptokinase and hirudin. The plasminogen-activating capacity of this streptokinase-hirudin complex is less than that of unmodified streptokinase by a factor of 8, however.
As noted above, plasminogen-activating amino acid sequences contain various domain sites which are well known and are described in the literature.
Urokinase and prourokinase comprise the following domains:
______________________________________ Domain Amino Acids Included ______________________________________ Growth Factor Domain amino acids 1 to 43 Kringle Domain amino acids 50 to 131 Serine Protease Domain amino acids 158 to 411 ______________________________________
See Guenzler et al., "The Primary Structure of High Molecular Mass Urokinase form Human Urine; The Complete Amino Acid Sequence of the A Chain", Hoppe-Seyler's Z. Physiol. Chem., 363, 1155-65 (1982); Steffens et al., "The Complete Amino Acid Sequence of Low Molecular Mass Urokinase from Human Urine", Hoppe-Seyler's Z. Physiol. Chem., 363, 1043-1058 (1982).
Tissue plasminogen activator comprises the following domains:
______________________________________ Domain Amino Acids Included ______________________________________ Finger Domain amino acids 4 to 50 Growth Factor Domain amino acids 50 to 87 Kringle 1 Domain amino acids 87 to 176 Kringle 2 Domain amino acids 176 to 262 Serine Protease Domain amino acids 276 to 527 ______________________________________
See Collen et al., "Thrombolytic and Pharmacokinetic Properties of Human Tissue-Type Plasminogen Activator Variants Obtained by Deletion and/or Duplication of Structural/Functional Domains, in a Hamster Pulmonary Embolism Model", Thrombosis and Haeomostasis, 65, (2), 174-180 (1991).
Bat-plasminogen activator comprises the following domains:
______________________________________ Domain Amino Acids Included ______________________________________ Finger Domain amino acids 1 to 43 Growth Factor Domain amino acids 44 to 84 Kringle Domain amino acids 92 to 173 ______________________________________
Serine Protease Domain amino acids 189 to 441 See Gardell et al., "Isolation, Characterization, and cDNA Cloning of a Vampire Bat Salivary Plasminogen Activator", Journal of Biological Chemistry, 264, (30), 17947-952 (1989).